1. Field of the Invention
The present invention relates to wireless broadcast sensor networks, and more particularly, to a method of controlling broadcasting between nodes configured in a wireless sensor network.
2. Description of the Related Art
WSN (Wireless Sensor Network) is a network configured with a sensor node for collecting information through a sensor, and a sink node for transmitting the collected information to an external network. Unlike a conventional network, the WSN is not used for a communication purpose, but is mainly used for an automated remote information collection and is widely used for development of various applications in scientific, medical, military, and commercial fields.
Most of the wireless sensor networks are configured with hundreds of nodes, and various time synchronizing systems are used to secure a uniform time period in each node by reducing time deviations. The time synchronizing systems include TPSN (Timing-synch Protocol for Sensor Network), RBS (Reference Broadcast Synchronization), and FTSP (Flooding Time Synchronization Protocol) systems, and the FTSP system is most frequently used.
The FTSP system is a time synchronizing system in which time information is transmitted to a network at a time point of transmitting a packet by using a time stamp, and an upper node receiving the packet corrects its local time by referring to the time stamp of the received packet. The upper node then broadcasts the corrected local time to a lower node configured in a wireless sensor network.
In the FTSP system, the upper node must broadcast for a short period to improve the accuracy of time synchronization between nodes configured in a wireless sensor network. In this case, the upper node broadcasts the time information regardless of the current status of a lower node, and thereby the energy efficiency of the total wireless sensor network may be decreased. Additionally, in the case of a wireless sensor network having a large number of nodes, a conventional FTSP system may limit the number of usable nodes and may have a disadvantage that the period of a power source replacement can be shortened.